Class Summarization BySecEngCL

8/8/2019 Class Summarization BySecEngCL

1/23

Class SummarizationClass Summarization

By English Section

Date: 7/01/11


2/23

ContentsContents

- ANCOVA

- Logistic Regression Analysis

- Effect Modification using GeneralizedEstimating Equation (GEE)

- Stratified Analysis and Test for trend


3/23

ANCOVA ANCOVA


4/23

ANCOVA

ANCOVA is a multivariate analysisUse for measuring the end points that are continuous variables. Forexample: value of fasting blood sugar

The assumption of ANCOVA is that the data is normally distributed.When the data are not normally distributed, the data must betransformed. For example by taking log natural.When we take log natural, geometric mean is presented (averagevalue of the natural logarithm of the data which will be closed tomedian)Need adequate number size (not low sample size)Use for one time point analysis (cross-sectional).


5/23

Box-and-whisker plots

Box-and-whisker plots can be used when the data is not normally distributed.

Advantages of the Box-and Whisker is that it will reflect:1. Deviation2. The highest & lowest 3. Median value4. IQR


6/23

Repeated ANCOVAIt is ANCOVA but can account for within and betweengroup comparisons, i.e., many time points in one analysisIt is used when1. more than 1 time points were compared and itsbaseline value of the study endpoint is put into the modelas the covariate.2. The result of between group difference is based on theaverage value of all time points (2 st , 3 rd and 4 th FBS )Repeated ANCOVA can tell us that there is at least onepoint difference between the two groups, however, it cannot tell that which particular points are exactly different.Therefore post-hoc like Dunnet test is required to find out which time point is the true different.


7/23

Logistic regressionLogistic regressionanalysisanalysis


8/23

Logistic regression analysisLogistic regression analysis

Logistic Regression is a type of predictive model that can be used when the target variable is a categoricalvariable with two categories for example

live/diehas disease/doesn t have disease


9/23

From lab page 24

Doxycycline versus Azithromycin for treatment ofLeptospirosis and Scrub Typhus

S tatistical analysisAll statistical analyses were performed by using SPSS (Aj.

told that it can be checked whether the authors got licenseor not).

P earson s or Fisher s exact test were used to compare ratesand proportions.

Man-Whitney U tests used to analyze continuous variablesthat were not normal distributed.

Independent sample t-tests were use to compare normallydistributed variables.

Time to fever clearance were compared using t-test.


10/23

From table 1, Demographic data, final diagnosis, andoutcome for all 296 patients included in the study

(intention-to-treat analysis)Notify that baseline and outcomes are in the same table

which is uncommon.

Outcomes composed of Median time to fever clearance(h)---using Man-

Whitney U testsNo.(%) for successful---using Fisher s exact test


11/23

Q uestion 19 : Which variables should be dependent variablefor the logistic regression?

Ans Logistic regression use for measure outcome which issuccess or not. S o the answer is rate of successful cases.If look at successful (in the table), Doxycyclin (95.6) and

Azithromycin (97.4) , the information means that most peoplehit endpoint (They get cured). Moreover, if we plot time to

fever clearance, they can use survival curve, the curve will godown (trend of curve is getting down to 1) , that meanseveryone cured from fever .

If the time to event is short, it might not be interesting to use

survival, so we use cumulative incidence.

Q uestion 20 : which variable should be covariates for thelogistic regression model?

Ans Gender, Age, No. of days of illness


12/23

From Lab page 25

Multiple comparisonDo the overall test ex. ANCOVA or repeated ANCOVA to

test the significant different.If you got significant, it mean they have at least 1 group is

different.Then, do post hoc test to prove that which pairs of

intervention have significantly different. This step has tocalculate new P -value to prevent type1 error.

If the test overall result is not significant, do not performthe post hoc analysis


13/23

Q uestion 21 : Are there differences between the groupsreceiving 12 mg/d vs 18 mg/d?

Ans we cannot answer from the information provided onthe table because they don t have information of 95% CI,which are the values that can be used to compare between12 and 18 mg/day groups. The information that they have is

the p value that compared each group with control (0mg/day). However, 95% CI can be calculated by usingequation per Aj. Areewan lecture (means + 1.96 SE ).


14/23

From Handout, page 14 , 1 st slide

Multiple logistic regression modelIt s brother of Chi-squareFollow up time of everyone is uniform. For instance,

everyone was followed up for 2 months.We will see OR that closely to RR, if event of interest is< 5%

RCT paper, we see hazard ratio (if they used Coxregression , OR (if they used logistic regression),however, interpretation of HR, OR are like RR.


15/23

Effect ModificationEffect Modification


16/23

The GEE (generalized estimating equation)

IT is used to evaluate the effect of variables ( age, sex,Fredickson type,familia hyperchloesteralemia,baseline value,week 4, 8 compared to 12 and two drugs) and interactions

o Repeated-measured analysis will use G EE

o Focus on estimating the average response over thepopulation rather than the regression parameters that wouldenable prediction of the effect of changing one or morecovariates on a given variable.

o It will show only overall average response of allpopulation but not specifically the differences of the twodrugs of each time point (except we put the interaction termin the model)>


17/23

Non-inferiority (Equivalent) are intended toshow that the effect of a new treatment is not worse than that of an active control by morethan a specified margin .

(it is hypothesized that new drug and old drug do not differalthough they do not yield the same effective

non-

inferiority trial non-inferiority trial


18/23

Clarify termnon-inferiority with 0 .1 equivalence margin

To determine whether the effective of two drugs aresignificantly different.

95%CI 1- 2 1- 2 0.1 10%

10% 2

10


19/23

From lecture note p . 15 Table 2

95% CI P itavastatin [1] P ravastatin [2]

95% CI Lower Upper limit Difference baseline 95% CI 0

95% CI [1-2]

TG 150 -10 pita pravas TG Non-inferiority TG 10% 10% -10 2 Non-inferiority equivalence margin


20/23

From lecture note p .16 F ig 2 .

From the mean percentage change of LDL P itavastatinwould decrease LDL level more than P ravastatin

From lecture note p . 16 F ig 3 .

from the mean percentage change of TG, P itavastatin

would decrease TG more than P ravastatin, especiallyWeek 4 and 8but for Week 12, the TG level of P itavastatin is finallyraising to the Baseline


21/23

Stratified Analysis &Stratified Analysis &Test for trendTest for trend


22/23

Test for trend

The test is to detect dose response relationship.To test whether the higher dose, the higher/lower response.Test for trend is very sensitive to get statistical significance if the higher levels have higher or lower responses although

95% CI of each category crosses 1 or 0.

According to the study distribution of IgA and IgG antibodytiters to C. pneumoniae among case and controls and

corresponding OR and 95%CI have presented titer 1:16and 1:64 opportunity lung cancer but we could not conclude that titer 1:64 have probably more opportunityoccur lung cancer than titer 1:16 because their 95% CIcrossed 1.


23/23

Strategy for statistical selection

Type of outcome

continuous Binary(yes/no)

Time toevent

Univariate T-test Chi-sq Survivalanalysis ,Log rank

Multivairatefor outcomemeasurement

ANCOVA,RepeatedANCOVA,

Generalizedlinear model

Logistic Cox

Class Summarization BySecEngCL

Documents

Transcript of Class Summarization BySecEngCL